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not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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site maintained by the Florida
Cooperative Extension Service.

Disease Management The Future In This Decade ........................
Emphasis on Disease Control Via Nutrition A Cultural Method of
Control ................ ......................... ..........
More Micro-irrigation or Subirrigation and Less Overhead
Watering .......... ..................... .....................
More Crop Scouting and Monitoring ..............................
Biological Control Agents for Soil Incorporation ..................
Disease Control by Climate Control in the Greenhouse ..............
Chemicals for Foliage and Soil Application ........................
Increased Management Input in Technology .......................
Forecasting Disease ..........................................

Integrated disease management involves merging activities into our production
programs that reduce the chances of introducing diseases (caused by pathogens
such as fungi, bacteria, viruses, viroids, mycoplasma-like organisms, etc.) into
the operation and which keep damages and losses to a minimum should problems
develop. For example, using resistant cultivars, keeping foliage dry (fungal
spores and bacterial cells develop in the presence of water), using proper
sanitation procedures, using plants produced through tissue culture procedures,
using plants grown from indexed stock plants, scouting to detect disease
outbreaks at an early stage of development, are just a few of the components
involved. A disease management program can be expected to function at its
maximum effectiveness only when all possible components are integrated into the
total production plan. A disease management program is only as good as its
weakest link.
1990'S THE DECADE OF THE ENVIRONMENT

Today's business must function in a world that includes many constraints. There
is an increased emphasis on protecting the environment. Americans want what they
perceive to be an improved quality of life. To this end, pesticides are singled
out feared by many as being a culprit even though pesticides are a minor risk
to health compared to many other factors such as smoking and automobile
accidents. The high fear- little risk scenario is present.

Many chemicals are used in the ornamentals industry; consequently there are
facets of our operations that have the potential to be detrimental to the
environment and to workers. Although we will always have a need for pesticides,
there are success stories of growing crops with fewer pesticides. We need to
intensively investigate and use non- pesticidal control methods when possible.
Our crops will be viewed more favorably by the buying public as we approach the
"utopian" organic concept of production. The recent media scare with the
chemical Alar demonstrated that an extremely low-risk but high-fear scenario
caused the public to overreact with the resultant dramatic reduction in product
sales (apples). Good judgement dictates that we expend our abilities to reduce
the need for pesticides and use improved disease management strategies.

In this decade, agriculture is confronted with many rules, regulations,
restrictions and laws, that pertain not only to pesticides but also to
fertilizer, people, water, etc. The social demands on agriculture continue to
increase and include such issues as water conservation, ground water pollution,
pesticide inspection, pesticide record keeping, pesticide residues, OSHA rules,
fertilizer and pesticide runoff, worker and health safety, re-entry requirements,
water quality standards, water-use permitting, soil conservation, Environmental
Protection Agency (EPA) rules, pesticide labels, and many others. We must be
knowledgeable about these issues and take an active role in shaping our industry
for the future. The rules and regulations are now a part of doing business.

INTEGRATED DISEASE MANAGEMENT IS IT TOO COMPLICATED?

We frequently hear such terms as epidemiological parameters, disease thresholds,
scouting procedures, complicated record keeping, etc. However, much of what we
can do in disease management is not complex but is simply common sense.
Following are examples of everyday procedures that can be conducted:

Some Common Sense Measures

Rubber gloves. Microorganisms (pathogens) can be carried on the hands and
transmitted to plants. Disposable rubber gloves are readily
available by the carton. They can be worn when transplanting,
potting, removing diseased plants, pruning tender plants, taking
cuttings, etc. to prevent spread of pathogens.

Diseased plants. Removal of diseased plants from greenhouses and
production areas should be done near the end of the workday. Place
diseased plants carefully in plastic bags at the site. Seal the bags
so airborne spores are not released into the air or soilborne
pathogens are not distributed from the bench to the dump site.
Employees should not handle apparently disease-free pots or plants
after handling diseased plants. Discard disposable rubber gloves
and wash clothes before returning to work the next day. People can
disseminate diseases unknowingly.

Washroom, sinks, soap, disinfectant. Place hand washing facilities
throughout production and transplant areas. Decontaminate hands by
washing with soap and/or disinfectant. Place signs in strategic
locations to remind and encourage employees to wash hands at regular
intervals.

Protect plants wash hands after eating! A sandwich may contain tomato,
lettuce, cucumber, squash, etc. These vegetables can carry Erwinia,
a bacterium that causes soft rot of many plants. The tomatoes may
have species of Xanthomonas, Pseudomonas and Corynespora which
infect tomatoes and peppers. There can be species of Alternaria and
Corvnespora which can infect many ornamental plants. Rhizoctonia,
Pvthium, and powdery mildew may be on the cucumber and squash.
Therefore, employees should wash hands after eating. They also
should wash in the morning when arriving, as some employees may have
worked in their own gardens prior to starting work and may be
carrying pathogens on their hands and shoes. Even nematodes can be
carried under the fingernails.

Flush water lines. Flush spaghetti tubes and water lines with a
disinfectant after finishing a crop. Many fungi and bacteria can
multiply and survive in water lines.

Floors, benchtops, walls of coldrooms and packing houses. Microorganisms
(pathogens) can be present or grow on organic debris on floors,
benchtops and walls (even walls in cold rooms). Sanitary conditions
can be maintained by flushing floors and benchtops at regular
intervals with a disinfectant. A low volume sprayer may be used to

spray walls and ceilings. Fungi such as Botrvtis, Alternaria and
Stemphylium may grow on walls.

Footbaths and equipment baths. Footbaths and equipment (tools) baths
placed at strategic points, especially outside stock areas, at the
entrance to tissue culture labs, production areas, or in locations
where plants are watered and fertilized by ebb and flow systems help
to reduce the spread of pathogens that are carried on soil particles
that adhere to shoes and equipment. Shallow baths for tractors serve
the same purpose.

Landscaping and flower beds. Flowering plants such as petunia, gerbera
and geranium should not be planted near packing houses and production
areas because they are excellent sources of airborne spores of
Botrytis, Alternaria, Stemphylium, etc. Spores can get into packing
boxes, production areas, etc. Flowering plants look nice but are
a potential hazard unless they are cleaned of senescent flowers and
leaves almost daily. Colorful foliage may be a better choice.

Weeds. Remove weeds under benches, around greenhouses, and around
production areas as they can harbor both pathogens and insects that
vector pathogens. Currently the widespread western flower thrips,
a vector for the destructive tomato spotted wilt virus, and the
sweetpotato whitefly, a vector for certain gemini viruses, are of
special concern. These insects infest weeds.

Transfer of diseased plant material via personnel or mail. Studying and/or
comparing diseased plant material with a neighbor should be done at
a non-production area. Pathogens and insects can be released into
the air or soil. Similarly, a special receiving area should be
established separate from production areas for receiving and
inspecting plant material that potentially may be diseased or be
infested with insects.

Communicate disease control strategy to employees with signs and short
company seminars. At strategic locations, place signs such as:

Wash hands with soap and water before handling plants.
Wash hands with soap and water at regular intervals when
transplanting.
Wash hands with soap and water at regular intervals when
disbudding or pruning.
Keep feet off benches.
Do not sit on benches.
Do not walk or sit on soil mix.
Hang up hoses.
Wash hands in the morning, after eating, and after
handling diseased plants.
Do not place flats of plants or pots on sterilized soil
in benches.
No Smoking viruses are present in tobacco products.

CULTURAL CONTROLS

Overseasoninq of Plant Pathogens.

Some pathogens overseason on diseased plant material. Diseased flowers, leaves,
stems and roots can harbor pathogens. In Florida, pot grown poinsettia plants
were cut off in January and the stems scattered under trees in an area adjacent
to the production site. Viable spores of Botrytis were still being produced the
following June. Many pathogens survive on and in plant tissue. The following
suggestions are made concerning the destruction and degeneration of inoculum on
plant tissue on the ground and in the soil.
Greenhouse and Shade House. Clean up, rake, and bag all plant debris
remaining after finishing a crop in a greenhouse, shade area, etc.
Also clean up plant debris in the area adjacent to the production
site. For example, Alternaria euphorbiicola, the cause of the
destructive Alternaria blight of poinsettia, produces in abundance
airborne spores on decaying leaves on the ground. Rototil or plow
under debris where possible.

Field Production. If a soilborne disease (Sclerotinia stem and flower
blight Sclerotium rolfsii southern blight, Cylindrocladium crown rot
and leaf spot, crown gall, Botrytis spp., Fusarium, etc.) were a
problem on the previous crop, remaining plant parts such as roots
and tubers should be dug and removed from the site without spreading
the diseased material around; it should be buried at a distant
location. The field should be rototiled or plowed at intervals until
the plant parts are decomposed. A minimum of 3 months after the
plant debris is decomposed is suggested as the minimum fallow period
before another crop is planted. Some pathogens die when they compete
with other microorganisms in the soil and the longer the fallow
period (including fallow to weeds) the greater the probability that
the pathogen has died. Of course, some pathogens, such as those
causing Fusarium wilt may live for many years in the soil.

Crop Rotation. Do not replant a problem field with the same crop. Make
the rotation as long as possible and do not replant with a highly
susceptible crop.
HIGH TECH ITEMS

Indexed Plants.

The ornamental industry is fortunate in that we have had procedures for years
in which certain crops such as chrysanthemums, geraniums, poinsettias, and others
are tested for freedom from fungi, viruses, bacteria, microplasma-like organisms,
etc. The indexed pathogen-free plants are increased in number to produce plants
for sale. Using plants produced from disease-free stock gives greater assurance
of not introducing disease into a crop or operation.

Tissue Cultured Plants.

Many varieties of plants are produced using tissue culture procedures. The
plants are available from many companies in many states. The plants are grown

under aseptic conditions and are free of disease. Using them is an excellent
way to practice non-chemical disease control.

Soils. "Mixes"and Composts.

Soilless mixes containing peat, perlite, vermiculite, sand, 'poly balls,' etc.
generally are free of pathogens. Many are available in large, plastic bags and
are thus protected from contamination. Suppressive soil mixes and/or composts
are becoming more readily available and contain natural biological organisms
which compete with pathogens. One generally has fewer pathogen problems than
with mixes that contain soil that has not been sterilized or pasteurized. Dr.
Harry Hoitink (Faber and Hoitink 1983, Hoitink 1980) from The Ohio State
University is a pioneer in the development of suppressive soil mixes and composts
and has spent many years studying the biology of these mixes and demonstrating
how they suppress pathogens. Non-composted mixes that contain soil or local
material, surface peats, or other organic, should be sterilized or pasteurized
before use.
Sticky Cards.

Sticky cards were developed primarily by entomologists. They usually are yellow
(many different kinds of insects are attracted by yellow) and contain a sticky
substance on which insects stick when they contact them. They are an excellent
way to determine what insects are present. Especially important are the western
flower thrips and sweetpotato whiteflies. The western flower thrips is a vector
for the tomato spotted wilt virus which infects many ornamental and vegetable
plants and is very destructive. Certain whiteflies, aphids and leafhoppers are
vectors for viruses which also can attack some ornamental crops. Using sticky
cards is, therefore, a good way to practice disease management by being
forewarned that insects are present that can be vectors for diseases or make
wound sites for the establishment of pathogens and subsequent disease.

Resistant Cultivars.

Using resistant cultivars when possible is an excellent non- chemical method of
disease control. When several cultivars are grown, and when some are known to
be very susceptible to, for example, a leaf disease or a soilborne wilt, certain
strategies should be followed such as planting the susceptible ones together in
one location so they can be given extra monitoring, extra sprays, special
treatments, and observation for early appearance of problems. This helps keep
disease to a minimum. Cultivars that consistently have disease problems should
be eliminated as soon as possible.
Treated Seeds.

Numerous fungal and bacterial pathogens are seedborne. When the seeds of a given
crop frequently are infested, seeds (or planting propagules) should be treated
either with an efficacious chemical or with a non-chemical treatment such as hot
water or aerated steam. Discontinue cultivars that are highly susceptible and
are consistently infected.

CHEMICAL CONTROL

Fungicides historically have been our major method of control for many plant
diseases. Generally, they can effectively control diseases caused by fungi and,
when mixed with copper fungicides, moderate control of diseases caused by
bacteria can be expected. Chemicals are not effective for the control of
diseases caused by viruses, viroids, mycoplasma-like organisms, etc. Fungicides
are currently a major method of control and it appears that in the future they
will continue to be needed for controlling plant disease. However, because of
the great concern for the environment and of the concerns of many people about
pesticides, great care must be exercised to use fungicides safely and wisely.

Resistant Strains of Pathogens.

One of the great concerns associated with some fungicides is the selection of
resistant strains of fungi (Ogawa 1989). Resistant strains are a problem with
systemic chemicals such as benomyl (Benlate), metalaxyl (Ridomil or Subdue),
iprodione (Chipco 26019, Rovral), and others. The basis for selecting resistant
strains is the variation among biological organisms. Charles Darwin wrote in
his book 'The Origin of Species' (1859) that species undergo modification and
therefore variation exists. In humans, for example, some people rarely catch
a cold while others catch a cold easily. Most fungous spores are killed easily
while an occasional one is resistant to a chemical. The occasional resistant
spore can then multiply and, in time, a new tolerant or resistant race of the
pathogen is built up. One of our responsibilities in using fungicides is to
manage the selection of fungicides in such a way that chemically resistant
strains are not selected. We can prevent or delay for an indefinite period the
selection of a resistant strain by using tank mixed combinations of two
fungicides, each at half the labeled rate, and then alternating different
tank-mixed combinations. Some of the combinations which can be used include:

These seven tank-mixed combinations represent seven different chemistries. The
same chemistry is not repeated in any of these seven tank-mix combinations. To
use these tank-mixed combinations correctly, one would need to identify the
disease that is present and then use fungicide combinations that will control
the disease and are labeled for the crop. Rotating the combinations (and hence
the chemistry) among the effective combinations precludes selecting a resistant
strain. Using this technique reduces the chances of selecting resistant races
of pathogens. If a spore is resistant it probably would be killed or inhibited
by the companion spray or by the next spray which is a different combination of
chemistries. The rates for these tank-mixes that we have found very effective
are one-half the labeled rate of each of the materials. Again, fungicides can
be used legally only on those crops listed on the label.

4

DISEASE MANAGEMENT THE FUTURE IN THIS DECADE

Emphasis On Disease Control Via Nutrition A Cultural Control Method.
Nutrition greatly influences the development of certain diseases, especially
Fusarium wilt (Engelhard and Woltz, 1973, 1988). It has been shown that Fusarium
wilt such as in chrysanthemum, aster, gladiolus, etc. can be greatly reduced by
maintaining the proper soil pH, using nitrate nitrogen rather than an ammonium
source of nitrogen, and drenching with the fungicide benomyl. These three
factors totally control Fusarium wilt on chrysanthemum and aster. Each of the
three factors gives a degree of control and any two are better than one. Other
diseases of the foliage and also of soilborne origin can be regulated by
nutrition (Engelhard 1989).
More Micro-Irrigation Or Subirriqation and Less Overhead Watering.

Most fungi need water to develop and cause disease. Overhead watering, rain,
and dew all facilitate disease development by fungi and bacteria. Without water,
fungous spores do not develop readily. Flow systems that introduce water from
below also keep the foliage dry.
More Crop Scouting And Monitoring.
The use of individuals who are trained in detecting and monitoring crops for
problems is increasing and will continue to do so in the future. With greater
pressure on reducing pesticide usage, emphasis is on early detection of problems
and quick solutions before large scale spraying is necessary. Growers should use
scouting techniques as a management tool.
Biological Control Agents For Soil Incorporation.

Research has been conducted for many years on the use of microorganisms to
control other microorganisms (pathogens) in the soil. Some success is in sight
and in this decade we should see one or more microbes that will be released for
use for the control of some of our common soilborne plant pathogens. The
microbes are expected to be available for both soil mixes and for greenhouse and
field soils.

Disease Control By Climate Control In The Greenhouse.

Proper moisture and temperature levels are critical for disease development
(Marois 1989). A critical combination of moisture, temperature and air velocity
can be established that is outside the parameters needed for a specific disease
to develop. The critical parameters can be monitored and when they approach the
range favorable for disease development, the temperature-wind velocity-moisture
parameters can be altered to stop impending disease development. The critical
parameters can be entered on computers and climate can be controlled
automatically. Small fans mounted overhead in greenhouses keep air moving
horizontally and reduce spore germination and disease development.
Chemicals For Foliage And Soil Application.

The trend will continue toward more precise application of chemicals at lower
volumes with more refined application methods and more accurately defined rates

to control disease, thus lowering the overall amount of pesticides used.
Chemicals for sterilizing soil outdoors will become increasingly scarce or
nonexistent, primarily because of potential contamination of water.
Increased Management Input In Technology.

In the future, management input in technology will be at a much higher level with
specialists (crop consultants) in plant pathology, entomology, irrigation,
nutrition, etc. playing greater roles in diagnosing problems and maintaining
product quality. Technology is expanding rapidly and it is becoming more
difficult for owners to keep up with new information as well as new rules and
regulations about pesticides and people. As competition increases and profit
margins are squeezed, the need to apply the latest technology increases in
importance.
Forecasting Disease.

The presence and number of spores, especially airborne spores, can be monitored
and used to indicate the potential for disease development. Such techniques will
be developed in response to resistance to the use of pesticides and/or scarcity
or unavailability of pesticides. The technique is in use on a number of
vegetable and fruit crops.

PRODUCT NAMES
Labels for products are changing and many products are undergoing reregistration.
Mention of a product does not imply that it is currently registered or that a
recommendation is being made for its use. Therefore, follow current label
directions for legal uses of fungicides. Product names are mentioned in this
publication solely for the purpose of providing specific information. Mention
of a product does not constitute a guarantee or warranty of its utility by the
Agricultural Experiment Station or an endorsement of one product or name over
another.